Objectives

1. Atmospheric Basics Objectives • Describe the composition of the atmosphere. • Compare and contrast the various layers of the atmosphere. • Identify three methods of transferring energy throughout the atmosphere. Vocabulary • exosphere • radiation • conduction • convection • ozone • troposphere • stratosphere • mesosphere • thermosphere

2. Atmospheric Basics Atmospheric Composition • Air is a combination of many gases, each with its own unique characteristics. • About 99 percent of the atmosphere is composed of nitrogen and oxygen, with the remaining one percent consisting of small amounts of argon, hydrogen, carbon dioxide, water vapor, and other gases.

3. Atmospheric Basics Atmospheric Composition

4. Atmospheric Basics Atmospheric Composition Key Atmospheric Gases • The amount of water vapor in the atmosphere can be as much as four percent of the atmosphere or as little as almost zero. • Carbon dioxide, another variable gas, makes up under one percent of the atmosphere. • The levels of both carbon dioxide and water vapor play an important role in regulating the amount of energy the atmosphere absorbs. • Water is the only substance in the atmosphere that exists in three states: solid, liquid, and gas.

5. Atmospheric Basics Atmospheric Composition Key Atmospheric Gases • When water changes from one state to another, heat is either absorbed or released which greatly affects weather and climate. • The atmosphere also contains solids in the form of tiny particles of dust, salt, and ice.

6. Atmospheric Basics Atmospheric Composition Ozone • Ozone (O3), is a gas formed by the addition of a third oxygen atom to an oxygen molecule (O2). • Evidence indicates that the ozone layer is thinning.

7. Atmospheric Basics Structure of the Atmosphere • The atmosphere is made up of several different layers. • Each layer differs in composition and temperature.

8. Atmospheric Basics Structure of the Atmosphere

9. Atmospheric Basics Atmospheric Composition Lower Atmospheric Layers • The troposphere, the layer closest to Earth’s surface, contains most of the mass of the atmosphere, including water vapor. • Most weather takes place in and most air pollution collects in the troposphere. • The troposphere is characterized by a general decrease in temperature from bottom to top. • The upper limit of the troposphere, called the tropopause, varies in height.

10. Atmospheric Basics Atmospheric Composition Lower Atmospheric Layers • The stratosphere, which is above the tropopause, is a layer made up primarily of concentrated ozone. • The stratosphere is heated because ozone absorbs ultraviolet radiation, and air gradually increases in temperature to the top of the layer, called the stratopause.

11. Atmospheric Basics Atmospheric Composition Upper Atmospheric Layers • The mesosphere is the atmospheric layer above the stratopause. • The top boundary of this layer is the mesopause. • The thermosphere is the atmospheric layer above the mesopause that contains only a minute portion of the atmosphere’s mass.

12. Atmospheric Basics Atmospheric Composition Upper Atmospheric Layers • The ionosphere, which is made up of electrically charged particles and layers of progressively lighter gases, is part of the thermosphere. • The exosphere, which is composed of light gases such as helium and hydrogen, is the outermost layer of Earth’s atmosphere. • There is no clear boundary between the atmosphere and space.

13. Atmospheric Basics Solar Fundamentals • The Sun is the source of all energy in the atmosphere. • This energy is transferred to Earth and throughout the atmosphere through radiation, conduction, and convection.

14. Atmospheric Basics Solar Fundamentals Radiation • The Sun is shining on, and therefore warming, some portion of Earth’s surface at all times. • Radiation is the transfer of energy through space by visible light, ultraviolet radiation, and other forms of electromagnetic waves. • While Earth is absorbing solar radiation, it is also continuously sending energy back into space.

15. Atmospheric Basics Solar Fundamentals Radiation

16. Atmospheric Basics Solar Fundamentals Radiation • The rate of absorption for any particular area varies depending on the physical characteristics of the area and the amount of solar radiation it receives. • Most of the solar radiation that travels through the atmosphere does so at short wavelengths, which are not easily absorbed. • Earth’s surface absorbs the solar radiation and then radiates energy with longer wavelengths, which warm the atmosphere through conduction and convection.

17. Atmospheric Basics Solar Fundamentals Radiation-Conduction-Convection

18. Atmospheric Basics Solar Fundamentals Conduction • Conduction is the transfer of energy that occurs when molecules collide. • Through conduction, energy is transferred from the particles of air near Earth’s surface to the particles of air in the lowest layer of the atmosphere. • For conduction to occur, substances must be in contact with one another. • Conduction affects only a very thin atmospheric layer near Earth’s surface.

19. Atmospheric Basics Solar Fundamentals Convection • Convection is the transfer of energy by the flow of a heated substance. • Pockets of air near Earth’s surface are heated, become less dense than the surrounding air, and rise. • As the warm air rises, it expands and starts to cool. • When it cools below the temperature of the surrounding air, it increases in density and sinks. • Convection currents are among the main mechanisms responsible for the vertical motions of air, which in turn cause different types of weather.

20. Atmospheric Basics Section Assessment 1. Match the following terms with their definitions. ___ radiation ___ conduction ___ convection B A C A. the transfer of energy that occurs when molecules collide B.the transfer of energy through space by visible light, ultraviolet radiation, and other forms of electromagnetic waves C.the transfer of energy by the flow of a heated substance

21. Atmospheric Basics Section Assessment 2. Label the layers of Earth’s atmosphere. Exosphere Thermosphere Mesosphere Stratosphere Troposphere

22. Atmospheric Basics Section Assessment 3. Why is ozone important? Ozone absorbs ultraviolet radiation from the sun. If ozone did not control the amount of ultraviolet radiation reaching Earth’s surface, our skin could not tolerate exposure to the Sun for very long.

23. End of Section 1

24. State of the Atmosphere Objectives • Describe the various properties of the atmosphere and how they interact. • Explainwhy atmospheric properties change with changes in altitude. Vocabulary • temperature • heat • dew point • condensation • lifted condensation level • temperature inversion • humidity • relative humidity

25. State of the Atmosphere Temperature Versus Heat • Temperature is a measurement of how rapidly or slowly molecules move around. • Heat is the transfer of energy that occurs because of a difference in temperature between substances. • Heat is the transfer of energy that fuels atmospheric processes, while temperature is used to measure and interpret that energy.

26. State of the Atmosphere Temperature Versus Heat Measuring Temperature • Temperature can be measured in degrees Fahrenheit (°F), in degrees Celsius (°C), or in kelvins (K), the SI unit of temperature. • The Kelvin scale measures the number of kelvins above absolute zero, a point where molecular motion theoretically stops.

27. State of the Atmosphere Temperature Versus Heat Dew Point • The dew point is the temperature to which air must be cooled at constant pressure to reach saturation. • Saturation is the point at which the air holds as much water vapor as it possibly can. • Condensation cannot occur until air is saturated. • Condensation occurs when matter changes state from a gas to a liquid.

28. State of the Atmosphere Vertical Temperature Changes • The temperature of the lower atmosphere decreases with increasing distance from Earth’s surface. • An air mass that does not exchange heat with its surroundings will cool off by about 10°C for every 1000 m increase in altitude. • The dry adiabatic lapse rate is the rate at which unsaturated air, to which no heat is added or removed, will cool.

29. State of the Atmosphere Vertical Temperature Changes • If the air is able to continue rising, eventually it will cool to its condensation temperature. • The lifted condensation level, or LCL, is the height at which condensation occurs. • The moist adiabatic lapse rate is the rate at which saturated air cools and ranges from about 4°C/1000 m in very warm air to almost 9°C/1000 m in very cold air.

30. State of the Atmosphere Vertical Temperature Changes

31. State of the Atmosphere Air Pressure and Density • The gravitational attraction between Earth and atmospheric gases causes particles of gas to be pulled toward the center of Earth. • Air pressure increases as you near the bottom of the atmosphere because of the greater mass of the atmosphere above you. • Atmospheric pressure decreases with height because there are fewer and fewer gas particles exerting pressure. • The density of air is proportional to the number of particles of air occupying a particular space.

32. State of the Atmosphere Air Pressure and Density

33. State of the Atmosphere Pressure-Temperature-Density Relationship • Temperature, pressure, and density are related. • In the atmosphere, temperature is directly proportional to pressure. • If an air mass maintains a certain density, as temperature increases or decreases, pressure does, too.

34. State of the Atmosphere Pressure-Temperature-Density Relationship • The relationship between temperature and density is inversely proportional. • If an air mass maintains a certain pressure, as temperature increases, density decreases, and as temperature decreases, density increases.

35. State of the Atmosphere Pressure-Temperature-Density Relationship • In most atmospheric interactions, however, neither density nor pressure remains unchanged. • Temperature varies with changes in both pressure and density. • Temperature is proportional to the ratio of pressure to density, which decreases with increasing altitude.

36. State of the Atmosphere Pressure-Temperature-Density Relationship Temperature Inversion • A temperature inversion is an increase in temperature with height in an atmospheric layer. • This can happen when the lower layers of the atmosphere lose heat to Earth’s surface and become cooler than the air above them. • A temperature inversion can act like a lid to trap pollution under the inversion layer. • In all cases, the presence or absence of inversions can have a profound effect on weather conditions.

37. State of the Atmosphere Wind • Air moves in response to density imbalances created by the unequal heating and cooling of Earth’s surface. • These imbalances, in turn, create areas of high and low pressure. • Wind can be thought of as air moving from an area of high pressure to an area of low pressure. • Wind speed generally increases with height in the atmosphere because there is less friction.

38. State of the Atmosphere Relative Humidity • Air in the lower portion of the atmosphere always contains at least some water vapor. • Humidity is the amount of water vapor in air. • Relative humidity is the ratio of water vapor in a volume of air compared to how much water vapor that volume of air is capable of holding.

39. State of the Atmosphere Relative Humidity • Relative humidity varies with temperature because warm air is capable of holding more moisture than cool air. • If the temperature of an air parcel increases and no additional water vapor is added, its relative humidity decreases. • If more water vapor is added to the parcel, its relative humidity increases.

40. State of the Atmosphere Relative Humidity • Relative humidity is expressed as a percentage. • If a certain volume of air is holding as much water vapor as it possibly can, then its relative humidity is 100 percent. • If that same volume of air is holding half as much water vapor as it can, its relative humidity is 50 percent, and so on.

41. State of the Atmosphere Section Assessment 1. Match the following terms with their definitions. ___ temperature ___ heat ___ dew point ___ humidity A D B C A. a measurement of how rapidly or slowly molecules move around B.the temperature to which air must be cooled at constant pressure to reach saturation C.the amount of water vapor in air D. the transfer of energy that occurs because of a difference in temperature between substances

42. State of the Atmosphere Section Assessment 2. What is the significance of 0 kelvin? Nothing can be colder than 0 K. This is called absolute zero and is the point where molecular motion theoretically stops.

43. State of the Atmosphere Section Assessment 3. Identify whether the following statements are true or false. ______ 1 m3 of air containing 5 g of water vapor has a higher relative humidity at 10ºC verses 20ºC. ______ As air flows down from a mountain, and its pressure increases, its temperature will fall. ______ Beyond the liquid condensation level, temperature generally increases. ______ Condensation cannot occur until air temperature reaches its dew point. true false false true

44. End of Section 2

45. Moisture in the Atmosphere Objectives • Explain how clouds are formed. • Identify the basic characteristics of different cloud groups. • Describe the water cycle. Vocabulary • condensation nuclei • orographic lifting • stability • latent heat • coalescence • precipitation • water cycle • evaporation

46. Moisture in the Atmosphere Cloud Formation • Buoyancy is the tendency for air to rise or sink as a result of differences in density. • Clouds form when warm, moist air rises, expands, and cools in a convection current. • Condensation nuclei are small particles in the atmosphere around which cloud droplets can form.

47. Moisture in the Atmosphere Cloud Formation • Orographic lifting occurs when wind encounters a mountain and the air has no place to go but up. • The air expands and cools resulting in cloud formation.

48. Moisture in the Atmosphere Cloud Formation • Cloud formation occurs with the collision of air masses of different temperatures. • As warmer air collides with cooler air, the bulk of it will be forced to rise over the more-dense, cold air. • As the warm air cools, the water vapor in it condenses and forms a cloud.

49. Moisture in the Atmosphere Cloud Formation Stability • How rapidly any given mass of air cools determines its stability. • Stability is the ability of an air mass to resist rising. • The rate at which an air mass cools depends in part on the temperature of the surface beneath the air. • Air can become unstable if it is cooler than the surface beneath it. • If temperature conditions are right and the air mass rises rapidly, it can produce the type of clouds associated with thunderstorms.

50. Moisture in the Atmosphere Cloud Formation Latent Heat • As water vapor in the air condenses, heat is released. • The energy to change liquid water into a gaseous state is stored in the water vapor. • Latent heat is stored energy in water vapor that is not released to warm the atmosphere until condensation takes place. • The amount of water vapor present in the atmosphere is a significant source of energy because of the latent heat it contains.